Photoelectric tube



Sept. 14, 1937. w. scl-lmFlaRnllcHTl PHOTOELEGTRIC 'TUBE' Filed Feb. 14,1936 INVENTOR WALTER SCHAFFERNICHT BY Wfl/Caza O'RNEY Patented Sept. 14,1937 PATENT oFFlcE rnocroELEo'rmc TUBE Walter Schaiernicht, Berlin,Germany, assignor to Allgemiene Elektricitats Gesellschaft, Berlin,Germany, a corporation 'of Germany Application February 14, 1936, SerialNo. 63,829 In Germany March 1, 1935 2 Claims.

According to the invention, this is accomplishedv l by means of afluorescent substance or material on the anode in the phototube, whichsubstance is made to glow by the photo-electrons released from thephotocathode by the impinging light, so that an increased release ofelectrons occurs.

:o The novel features which I believe to be characteristic of myinvention are set forth with particularity in the appended claims, butthe invention itself will best be understood by reference to thefollowing description taken in connection with the accompanying drawingin which the Figure 1 is a schematic representation of a phototube insection embodying-my invention and its associated circuit, and Figure 2is a schematic representation of a modication of my invention. :in Inthe figure, the envelope I of the phototube contains the photocathode 2and oppositely disposed anode 3. The photocathode may be any of theconventional type cathodes and may have any of thc usual structuralshapes and may con- .",5 sisi; of a special plate, as shown, or it maybe deposited on the wall of the vessel. Likewise, the anode may be ofany shape other than that shown. According to the invention a layer 4 offluorescent material is applied to the anode. The cathode l0 and anodeare connected in the conventional manner, to the positive and negativepoles of a voltage supply battery 5 across the load 6. .If light fallsfrom the outside on the cathode, photoelectrons will be liberatedtherefrom which im- 45 pinge on and bombard the anode after beingaccelerated by the anode potential. The kinetic energy of thephoto-electrons will thereby be transformed into light by thefluorescent layer .or coating 4, and this light will in turn add to theilluminations of the cathode thereby releasing more photo-electrons fromthe cathode. This action which may be designated as an optical feedback, may under suitable selection of the operating conditions besuccessively repeated re- CII sulting in an extremely high increase inthe (Cl. Z50-27.5)

photo-electric current. The photo-electric current can be increased byone hundred to one thousand times its initial value. It is desirable tohave the cathode or the anode or both formed as concave surfaces wherebythe concave sides face each 5 other which can be accomplished in anespecially simple manner when the electrodes are deposited oncorrespondingly curved parts of the wall of the vessel as shown inFigure 2. In this arrangement, dispersion of the photo-electrons aswellas of the light in lateral direction will be avoided, so that allprimary, secondary, and other photoelectrons will impinge on the anode,and the entire fluorescent light rays will be directed upon the cathode.

It is also possible to provide electron-optical reproducing elementssuch as electrical or magnetic elds or both, by means of which thephotoelectrons will be directed into desired paths. In the figure thereis shown for example for this purpose a coil 1 in cross section whichsurrounds the electron path. An especially large amplication will beobtained if the fluorescent substance is so chosen that its range ofemission comes within the maximum spectral sensitivity of thephotocathode.

Finally it may be advisable for example in view of the path of rays ofthe primary light, to arrange the iluorescent layer 4 separate from theaccelerating anode 3 for instance in such manner 30 that the anode isformed as a grid or net and placed between the cathode Z' `and theuorescent layer 4. Also in this case the anode accelerates thephoto-electronsv to such velocity that its energy content causes theuorescent layer 4' to 35 glow. In this case the layer 4 will beelectrically connected in a suitable manner for example by conductor 8with the anode, so as to avoid disturbing space charges. With respect tothe path of rays of the primary light it may eventually be 40 advisableto provide a transparent cathode 2' so that the primary light can beradiated thereon from the rear.

If fluctuations of light which vary very rapidly are to be transformedinto electric current, the inertia, of the iluorescence, i. e. the slowdyingout of the luminescence may produce a disturbing effect. In thiscase it will be of advantage to provide means such as a heating resistor9 which may be against the envelope I for heating the iiuorescent layerso that the dying-out period will be much shortened.

Finally, in the application of the idea of the invention it isimmaterial whether the phototube is highly evacuated or whether a gasfilling is provided.

The inventive idea can be correspondingly applied to any type ofphototube other than described and shown. Thus it is possible to alsocorrespondingly apply the feed back to blocking layer or resistancecells.

It is obvious that if desired, the high power photo-currents-produced inthis way within the tube may also be further amplified by additionalamplifier arrangements.

While I have indicated the preferred embodiments of my invention ofwhich I am now aware and have also indicated only one specificapplication for which my invention may be employed, it will be apparentthat my invention is by no means limited to the exact forms illustratedor the use indicated, but that many variations may be made in theparticular structure used and the purpose for which it is employedwithout de parting from the scope of my invention as set forth in theappended claims.

What I claim as new is,-

1. A phototube having an elongated tubular envelope having closed endsproviding concave surfaces facing each other, a photocathode on one ofsaid concave surfaces and a fluorescent layer on the other concavesurface of said envelope, and an anode, within said envelope, said anodeand fluorescent layer being electrically connected.

2. A phototube having an elongated tubular envelope having closed endsforming concave surfaces facing each other, a photocathode on one ofsaid concave surfaces and a fluorescent coating on the other concavesurface of said envelope, and an anode Within said envelope, said anodeand fluorescent coating being electrically connected, and means forheating the fluorescent coating.`

WALTER SCHAFFERNICHT.

